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Aqa chem 4/ chem 5 june 2016 thread

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Original post by flylikeafly
like asking us about things that I may have missed in the book or thought was never come up based on past papers.


I'm doing the same! If you find anything weird do you mind posting it here please?
http://filestore.aqa.org.uk/subjects/AQA-CHEM5-QP-JUN13.PDF
For 2cii) why do you times 0.0607 by 17.2?
Reply 2042
Original post by zombaldia
Lattice dissociation: bonds are breaking: Bond breaking releases energy: It is always positive!!


hm im pretty sure bonds forming release energy and u have put in energy to break bonds so bonds breaking would take up energy
Original post by SirRaza97
I haven't doubled the temp. I have doubled the enthalpy change. This is because in the second equation I am creating 2 lot's of water. So the energy required to create twice the amount will be twice the energy so deltaH is multiplied by 2.

In the first equation whichis how the mark scheme does it, is that you are creating 1 mol of water so deltaH is -242. The reason it's half of water because the first equation is 1/2O2 which means that the entropy must be half aswell.


Safe.

Do you mind explain the strength of the Cl-Cl bond compared to a br-br bond?
Original post by GO97
hm im pretty sure bonds forming release energy and u have put in energy to break bonds so bonds breaking would take up energy


I agree with this.

Lattice enthalpy required bond forming between gaseous ions bond forming is negative

And hydration reauires bond forming with h2o which is also negative
what is formed when a solution containing Al3+ is reacted with excess OH-? [Al(OH)4]- or [Al(OH)6]3-

I've seen both
Original post by rolla01
what is formed when a solution containing Al3+ is reacted with excess OH-? [Al(OH)4]- or [Al(OH)]3-

I've seen both

the book says 4
Original post by flylikeafly
what should I revise? Any predicitons


everything its not that big compared to chem4
Original post by Super199
Safe.

Do you mind explain the strength of the Cl-Cl bond compared to a br-br bond?


Sure no problem. The Cl atom is smaller compared to bromine and has less electron sheilding due to less shells around the atom. So the attraction between the nuclues of the chlorine atom and the bond pair of electrons is much stronger because the distance between them is smaller. (Think of it like two magnets attracting. The closer they are the stronger they attract and so the harder it is you pull them away from each other).

Thus the energy required to overcome this force is much greater. So Cl-Cl bond has requires more energy to break than Br-Br bond.
Original post by rolla01
what is formed when a solution containing Al3+ is reacted with excess OH-? [Al(OH)4]- or [Al(OH)6]3-

I've seen both


Book isn't always right but

Is say al oh6

Cause coordination number seems to be based on size of the molecules / atoms so similar size things will have the same coordination number

So nh3 oh h20 and cn should all have coordination number of 6

Where cl will have 4
If Delta G is less than or equal to 0 do you say that the reaction is feasible or that it is spontaneous? Or does it not matter? I've seen both appear in markschemes so idk :/
Only starting to revise tonight, am I doomed?
Original post by lahigueraxxx
If Delta G is less than or equal to 0 do you say that the reaction is feasible or that it is spontaneous? Or does it not matter? I've seen both appear in markschemes so idk :/


i always write both tbh just to make sure
Original post by nutcase13
i always write both tbh just to make sure


Ah okay cool - thanks! :smile:
Original post by lahigueraxxx
If Delta G is less than or equal to 0 do you say that the reaction is feasible or that it is spontaneous? Or does it not matter? I've seen both appear in markschemes so idk :/


Feasibility is talking about the likely hood it is going to be spontaneous a requirement is it has to be below 0 for spontaneous reactions however if they ask why it is below 0 and not spontaneous it wants you to talk about high activation energy etc
How do you do this question
June 2012 question 6di
I thought you can't combine three redox equations?
ImageUploadedByStudent Room1466534163.873380.jpg


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Original post by Chembio123
Only starting to revise tonight, am I doomed?


If I were you I'd pull an all nighter
Original post by YoloSwagginz
Feasibility is talking about the likely hood it is going to be spontaneous a requirement is it has to be below 0 for spontaneous reactions however if they ask why it is below 0 and not spontaneous it wants you to talk about high activation energy etc


Thanks! :smile:
Reply 2058
Original post by Bloom77
How do you do this question
June 2012 question 6di
I thought you can't combine three redox equations?
ImageUploadedByStudent Room1466534163.873380.jpg


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You're not combining them, you're finding the ratio

MnO4- will stay on one side
Original post by Jmedi
You're not combining them, you're finding the ratio

MnO4- will stay on one side


And how would you do that
I normally combine them to find the ratio like you know for those maths chem questions at the end


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